This invention relates to polyethers containing an antioxidant, as well as polyurethanes made from such polyethers.
Polyethers are used in a great number of applications, particularly aliphatic polyethers, are prone to oxidation, which results in degradation of the polyether, and in polyurethanes made therewith.
Thus, many polyethers are sold as blends containing an antioxidant package. The antioxidant most commonly used in polyethers is 2,6-di-t-butyl-4-hydroxytoluene (BHT, or a mixture of antioxidants of which BHT is a major component. BHT is typically used at a level of 3000-5000 ppm, based on the weight of he polyether, even when additional antioxidants are used.
Although BHT is an effective antioxidant, its use has several drawbacks. Antioxidants are generally used in small quantities, and so must be metered accurately into the polyether to provide optimal levels. This is made difficult with BHT, since it is a solid and is therefore difficult to meter accurately.
More importantly, BHT is volatile, which causes some significant problems. When making polyurethanes, especially flexible foams, high temperatures are encountered during the foaming process. These high temperatures cause the BHT to vaporize and escape from the foam. Thus, a significant portion of the BHT is lost. The effect of this loss is seen in two ways. Portions of the foam degrade due to the exotherm from the foaming process. The foam may also be subject to a slower degradation over time.
The degradation of the foam results in a loss of physical properties. In many cases, this loss of physical properties is such that large portions of the foam, and perhaps the entire foam, is unusable. In extreme cases, the foam can catch fire. The degradation may also manifest itself by discoloring the foam, which is in itself a very substantial problem. Many foams must be very white for cosmetic purposes. Other foams are dyed to indicate their grade. In those instances, the discoloration forms undesirable conjugate colors with the dyes.
Another problem with BHT is that although solid, it sublimes. The BHT that is not lost during foam formation tends to sublimate. In many furniture, carpeting and automobile applications, the foam is in contact with a fabric or plastic film. The BHT which sublimes often discolors this material.
Thus, it is desirable to provide an effective antioxidant for polyethers which is less volatile than BHT. It is further desired to provide an antioxidant for polyethers which will inhibit loss of physical properties in a polyurethane made from the polyether. It is even more desirable that the antioxidant also inhibit discoloration in the polyurethane. In addition, it is further desired to provide a liquid antioxidant for polyethers.